ArticlePDF Available

Low Concentration and High Transparency Keratin Hydrogel Fabricated via Cryoablation


Abstract and Figures

Keratins are highly attractive for medical applications due to their inherent self-assemblies characteristics and biocompatibility. However, nearly all researches have focused on the properties of hybrid hydrogels which was prepared from human hair keratin with other materials, and the preparation methods and properties of pure keratin hydrogels are rarely studied. Thus, we extracted keratins from rabbit hair, and a low concentration and high purity RHK hydrogel was then prepared by a simple freeze–thaw cycle and used to study gelation and the optical properties. The results indicated that RHK keratin hydrogel is a reversible thixotropic system and elastic modulus the storage modulus (G′) substantially improves with freeze–thaw cycles. The systematic assessments including microstructural observation, porosity, and the secondary structure confirmed that the structure and properties of keratin hydrogels can be changed by controlling freeze–thaw cycles. Meanwhile, it is found that RHK hydrogel had high optical transmittance, and still maintained its fluorescent properties, which would be useful to observe the wound healing and locate the drug delivery process.
Content may be subject to copyright.
Low Concentration and High
Transparency Keratin Hydrogel
Fabricated via Cryoablation
Xiaoqing Wang
, Zhiming Shi
*, Le Zhao
and Xianyi Shen
School of Materials Science and Engineering, Inner Mongolia University of Technology, Hohhot, China,
College of Textile and
Light Industry, Inner Mongolia University of Technology, Hohhot, China
Keratins are highly attractive for medical applications due to their inherent self-assemblies
characteristics and biocompatibility. However, nearly all researches have focused on the
properties of hybrid hydrogels which was prepared from human hair keratin with other
materials, and the preparation methods and properties of pure keratin hydrogels are rarely
studied. Thus, we extracted keratins from rabbit hair, and a low concentration and high
purity RHK hydrogel was then prepared by a simple freezethaw cycle and used to study
gelation and the optical properties. The results indicated that RHK keratin hydrogel is a
reversible thixotropic system and elastic modulus the storage modulus (G) substantially
improves with freezethaw cycles. The systematic assessments including microstructural
observation, porosity, and the secondary structure conrmed that the structure and
properties of keratin hydrogels can be changed by controlling freezethaw cycles.
Meanwhile, it is found that RHK hydrogel had high optical transmittance, and still
maintained its uorescent properties, which would be useful to observe the wound
healing and locate the drug delivery process.
Keywords: keratin hydrogels, freezethaw, rheology, morphology, optical properties
As a renewable resource, keratin resources are very abundant, it is found widely in human and animal
organs, including epidermis, hoof, horn, hairs, feather, and protein ber (Shavandi et al., 2017). For a
long time, people have been working on extracting keratin from ber, studying its biocompatibility
and degradability for tissue engineering and medical applications (Esparza et al., 2018a), such as
wound healing (Wang et al., 2017;Kim et al., 2019;Konop et al., 2020), hemostatic dressings (Sun
et al., 2018;Tang et al., 2021), controlled drug delivery (Guo et al., 2014;Nakata et al., 2015;Sun et al.,
2016), and antibacterial wound dressing (Zhai et al., 2018;Sadeghi et al., 2020). Using a riboavin-
SPS-hydroquinone (initiatorcatalystinhibitor) photosensitive solution, Placone and others
prepared keratin scaffolds through 3D printing technology (Placone et al., 2017). Despite these
advantages, these biomaterials are mainly prepared from keratin mixed with other materials because
pure keratin template has poor mechanical properties. The tensile strength and elongation of the
keratinsodium alginate scaffold were intensively studied by Gupta and Hartrianti (Gupta and
Nayak 2016;Hartrianti et al., 2017). However, the introduction of other substances may reduce the
biocompatibility of the eventual scaffold.
Some studies have tried to make pure keratin scaffolds (Saul et al., 2011;Burnett et al., 2013;Wang
et al., 2015), but most of the preparation and research of hydrogels has focused on human hair.
However, the color of hair might vary considerably and contain a variety of chemical dye
Edited by:
Helan Xu,
Jiangnan University, China
Reviewed by:
Junheng Zhang,
South-Central University for
Nationalities, China
Bihe Yuan,
Wuhan University of Technology,
Zhiming Shi
Specialty section:
This article was submitted to
Polymeric and Composite Materials,
a section of the journal
Frontiers in Materials
Received: 15 May 2021
Accepted: 19 July 2021
Published: 19 August 2021
Wang X, Shi Z, Zhao L and Shen X
(2021) Low Concentration and High
Transparency Keratin Hydrogel
Fabricated via Cryoablation.
Front. Mater. 8:710175.
doi: 10.3389/fmats.2021.710175
Frontiers in Materials | August 2021 | Volume 8 | Article 7101751
published: 19 August 2021
doi: 10.3389/fmats.2021.710175
composition; in addition, there are high concentration of keratin
solution and poor formability of pore. It is well known that the
efciency of extracting keratin is low, which greatly limits the
industrial process of preparing hydrogels with keratin. Therefore,
it is particularly necessary to nd suitable keratin resources and
prepare keratin gel with low concentration and high purity by
environmentally friendly methods.
As a simple and clean technique for preparing hydrogels,
cryogelation has been used more and more. The preparation of
keratin hydrogels by cryogelation is mainly based on the self-
assembly of keratin. The solvent crystallizes when the
temperature is below freezing point, and the keratin
macromolecules combine with each other by disulde bonds,
hydrogen bonds, hydrophobicity, electrostatic attraction, and van
der Waals forces (Esparza, 2018b), when the temperature returns
to above freezing point, as the solvent crystals melt, solvent and
other components are enveloped in a three-dimensional network
of keratin, an interconnected microporous hydrogel structure is
formed (Lozinsky 2002;Henderson et al., 2013). In a recent study
by Chua et al. (Cui et al., 2019;Chua et al., 2020;Zhao et al., 2020),
HHK sponges was prepared by this method. However, as with
previous studies, the main research focuses on the mechanical
and biocompatibility of hydrogels, whether pure or hybrid keratin
Herein, keratin extracted from rabbit hair with rich resources,
high amino acid content and poor spinnability was used as the
research object, a low concentration, high purity, and transparent
keratin hydrogel was prepared by simple freezethaw (FT) cycle.
It has been conrmed that the extracted rabbit hair keratin is
nontoxic. In this study, the feasibility of preparation of rabbit hair
keratin (RHK) hydrogel by cryogelation was studied. The
morphology and structure of RHK hydrogel were tested, and
the optical properties of keratin were comprehensively evaluated.
Rabbit hairs were collected from German Angora rabbit warren
(Gansu, China). Urea and sodium bisulte were purchased from
Damao chemical reagent Co. Ltd (Tianjin, China). Sodium
dodecyl sulfate (SDS) was purchased from Usolf Co. Ltd.
(Shenzhen, China).
Preparation of Rabbit Hair Keratin
RHK was extracted according to literature (Wang et al., 2021),
with modications. Briey, the rabbit hair defatted with
petroleum ether and anhydrous ethanol was subjected to
ultrasonic treatment. And then, it was immersed in mixed
urea-sodium bisulte-sulfate solvent, and the solution was
heated and mechanically stirred for 4.5 h. The solution was
ltered to remove the undissolved rabbit hair, and the
obtained rabbit keratin solution was subsequently dialyzed in
distilled water using a dialysis tube for 48 h to remove small
molecules and salt formed in the reaction; during which, the
distilled water was changed every 4 h. The dialysis solution was
stored at 4°C for the following experiments.
FreezeThaw Cycles for Rabbit Hair Keratin
Dialyzed solution with mass concentration of 2% was kept in a
refrigerated circulating device at 20°C for 12 h, thawed at 4°C,
and then the RHK hydrogel was prepared after several FT cycles.
The hydrogel was freeze-dried at 80°C to prepare keratin
scaffolds for morphology and structure testing, and the RHK
solution without the FT treatment was used as control.
Characterization and Measurements
Oscillatory rheology: The self-assembly gelation and the change of
rheological characteristics during reversible phase transition of
keratin hydrogels were characterized using a rheometer (Anton
Paar MCR92, Germany). RHK hydrogels were cast in 25 mm Petri
dishes. The oscillatory frequency sweep experiments were
performed at angular frequency of 0.1100 rad/s at a constant
strain of 1% at 25°C, and the elastic modulus (G) and viscous
modulus (G) were recorded. The apparent viscosity change of
50 mL keratin solution during gelation was measured using a
rheometer (Brookeld R/S Plus Rheometer, United States) at 25°C.
Scanning electron microscopy (SEM): The RHK scaffold was cut
into thin slices with a sharp knife to expose clean cross sections.
Samples were gold-sputtered at 18 mA and observed using a
scanning electron microscope (650 FEG, FEI Quanta) at an
accelerating voltage of 20 kV under high vacuum. We
characterized the pore size within the hydrogel microarchitecture
from the SEM images using image processing techniques.
Porosity measurement: The porosity of the RHK scaffold was
tested using a liquid displacement method with absolute ethanol
(Loh and Choong, 2013). Briey, put the RHK scaffold into a certain
volume (V
) of ethanol and record the volume (V
after 1 h. Next, the liquid-impregnated scaffold was removed, and
the remaining liquid volume (V
) was recorded. The porosity of the
RHK scaffold was calculated according to Equation (1) as follows:
Fourier transform infrared spectroscopy: Chemical structures
of RHK hydrogels and RHK were characterized using a Fourier
transform infrared (IR Afnity-1 FTIR, Shimadzu) spectroscope
operated in the transmission mode. The FTIR spectra were
recorded at a wave number range of 4,000 cm
to 400 cm
at a resolution of 4.0, and at 40 scans per sample.
Raman spectroscopy: Raman spectra were obtained via a
Raman microscope (INVIA REFLEX03040404, Renishaw). The
laser excitation was provided with an argon ion laser operating at
10.2 mw of 633 nm output. Spectra were recorded between 2,000
and 300 cm
. For each sample, about three replicates were
X-ray diffraction: Crystal structures of RHK hydrogels and
RHK were determined by X-ray diffractometer (D/MAX-2500/
PC XRD, Rigaku) operated using a Cu Kαradiation source. The
samples were scanned at a 2αBragg angle range of 5°60°at 0.02°
step size and a scan speed of 3°/min.
Optical properties: The transmittance of RHK samples was
measured by UV-visible spectrophotometer (UV-2700,
Shimadzu). The scanning range is 300800 nm. Endogenous
Frontiers in Materials | August 2021 | Volume 8 | Article 7101752
Wang et al. Keratin Hydrogel Fabricated via Cryoablation
uorescence spectra of proteins were determined at room
temperature using uorescence spectrophotometer (G9800A,
Agilent). The excitation wavelength is 300 nm, and the
scanning range is 300550 nm.
Measurement of particle size distribution: The particles size
distribution of RHK butadiene was determined by dynamic laser
scattering at 25°C.
Compressive measurement: Keratin hydrogels were prepared
into cylinders with a diameter of 10 mm and a height of 13 mm.
Uniaxial compression was conducted at RT using a universal
mechanical tester (Shimadzu, Japan) with 30 kN load cell. The
cross-head speed was set at 0.1 mm/min and the tests were
Rheological Properties of Rabbit Hair
Keratin Hydrogels
The gelation process of low concentration RHK solution was
illustrated in Figure 1A. The RHK solution self-assembled into
hydrogels without the adding of any chemical cross-linking agent
under FT cycles. The transparent and owing RHK solution was
gradually converted to a semi-solid gel state through two FT
cycles. With the continuation of FT, RHK solution forms a single
highly transparent, intact piece of gel with a three-dimensional
network structure. The RHK hydrogel (FT3)broken by shearing
can form the initial gel state after being cultured at 20°C for 12 h
(Re-gel). From this knowable, RHK hydrogel is a reversible
thixotropic system. Noticeable feature is the absence of distinct
phase separation between the keratin hydrogels and the
surrounding aqueous medium as the article says (Zhao et al.,
2020). We believe that the formation of keratin hydrogels is due
to the three-dimensional network structure formed by the
binding of keratin molecules, bound water adsorbed by keratin
hydrophilic groups, and the unbound water clamped in the pore
In order to further elucidate the rheological properties of low-
concentration RHK solution during FT cycles, the apparent
viscosity, G, and Gmeasurements were performed on the
RHK samples. In Figure 1B, comparative analysis between
RHK samples after different FT cycles shows that the apparent
FIGURE 1 | (A) Gelation and Reversible transformation of RHK, (B) viscosity and, (C) oscillatory amplitude sweep measurement of RHK samples at varied FT
Frontiers in Materials | August 2021 | Volume 8 | Article 7101753
Wang et al. Keratin Hydrogel Fabricated via Cryoablation
viscosity of RHK solution did not change and was almost zero,
this is consistent with the actual gelation phenomenon
(Figure 1A-FT1) after one FT cycle. The apparent viscosity of
the RHK hydrogels increased with the number of FT cycles after
FT2. For all samples, the apparent viscosity decreased with
increasing shear rates, suggesting a shear-thinning behavior
that is typical of viscoelastic uids and gels, which could be
attributed of weak interactive forces or chain entanglements
between RHK at high shear rates.
Gis used to evaluate the strength or solid-like behavior of
hydrogels. It is related to the ability of material to store energy and
return to its original shape after being subjected to stress.
Assessment on the viscoelastic properties of hydrogels (FT3,
FT6, and FT9) and re-gel sample was conducted with
oscillatory rheology (Figure 1C). The experiments show that
the Gis signicantly higher than G, thereby suggesting that
these samples behave more like a viscoelastic gel rather than a
viscous uid (Fu et al., 2020). Furthermore, Gincreased with the
FT cycles, with the highest recorded value of 2,483.3 Pa in FT9
samples, which indicated that the rheological properties of the
hydrogels depended on the FT cycles. It is interesting that the G
and Gof re-gel sample were higher than that of FT3 samples,
and it can be seen that the shear force cannot cause irreversible
rupture of the keratin hydrogels.
Rabbit Hair Keratin Scaffolds Morphology
Bioporous materials not only provide space for cell proliferation
and survival (Wang et al., 2012) but also provide a
microenvironment for the maintenance and release of bioactive
molecules (Chen and Mooney 2003). To further elucidate the
correlation between macroscopic behavior and micro
morphology, the morphologies of RHK scaffolds freeze-dried at
80°C with different FT cycle were shown in both low- and high-
magnication SEM images (Figure 2A). The morphologies of
RHK solution sample freeze-dried at 80°C presented obvious
lamellae albeit structure, but the morphology of RHK scaffolds
appears to have regions of regular porous structure with
interconnected pores. Cui et al. (2019) prepared the hydrogel
with 20 mg/ml pure human hair keratin solution, which is the
relatively low concentration used for preparation of keratin
hydrogel at present. However, the microstructural imaging
shows that the porous structure of keratin hydrogel is incomplete.
Ge et al. (2021) prepared rabbit hair keratin with L-cysteine
hydrogel by the heating and cooling method, and the keratin
FIGURE 2 | (A) SEM images, (B) pore size distribution, and (C) porosity.
Frontiers in Materials | August 2021 | Volume 8 | Article 7101754
Wang et al. Keratin Hydrogel Fabricated via Cryoablation
hydrogel showed an uneven porous structure. The shape of the
hole gradually changes from approximately round to rectangular
as FT cycles increases, and even to ake. At the same time, the
wall thickness of the hole also increases gradually. This
distinction in morphology is evident in FT3 and FT9 samples.
It can be inferred that the formation of columnar ice crystals
affects the shape of keratin hydrogel pores during FT processes.
The damaged hydrogels are still able to maintain intact porous
structures after the FT cycle.
The maximum distance of each hole was selected for the test
because the shape of hole of the FT9 scaffolds tends to be
rectangular. Figure 2B shows that the aperture of the three-
dimensional keratin scaffold increases with the FT cycles.
Apertures of the keratin scaffolds were 127 um, 232 um, and
324 um, respectively. Figure 2C shows that porosity of the keratin
scaffold is as high as 92%. In addition, FT cycles have a signicant
effect on aperture, but had no obvious effects on the porosity of
keratin scaffolds. After vacuum freeze drying, the moisture
content directly affects the porosity because the keratin
hydrogels gradually dehydrate to form a sponge scaffold. As
can be seen from Figure 1, there is almost no water loss in
the process of FT cycles, so the volume of hydrogels had little
change after forming, which may be the reason why the FT cycles
have little inuence on the porosity.
Structure of RHK Hydrogels
The FTIR spectra of RHK samples were observed in the range of
4004,000 cm
(Figure 3A), where they could be assigned to the
stretching vibrations of NH, which occurs in the range of
3,200500 cm
(Amide A), the stretching vibration CO which
fall at 1,654 cm
(Amide I), the out-plane bending vibration of
NH and CH stretching which falls in 1,4801,580 cm
II), and the in-phase stretching vibration of CN which fall at
1,238 cm
(Amide III) (Zhang, Zhao, and Yang 2015).
Functional groups and chemical bonds were generated after
the FT treatment of keratin solution. The amide I region of
the infrared spectrum of keratin is shown in Figure 3B. It can be
seen that the typical absorption peak at amide I region 1,654 cm
of the infrared spectrum of keratin corresponds to the
intermolecular βfolding structure. After FT cycle, the position
of the absorption peak did not have any deviation. Compared
with amide I, amide II band is mainly sensitive to environmental
changes of the NH group. Therefore, the amide II band can be
used to infer changes in the hydrogen bond microenvironment.
FIGURE 3 | (AB) The FTIR spectra of RHK samples, (C) Roman spectra, and (D) XRD.
Frontiers in Materials | August 2021 | Volume 8 | Article 7101755
Wang et al. Keratin Hydrogel Fabricated via Cryoablation
Belton studies have found that strong NH hydrogen bond
groups are absorbed at high frequencies, that is, the stronger
the high wave number absorption, the more the hydrogen bond
groups are (Belton et al., 1995;Almutawah et al., 2007). As can be
seen from Figure 3B, compared with RHK solution, the
absorption peak of RHK hydrogels at 1,543 cm
signicantly higher than that at 1,523 cm
, indicating that
hydrogen bond association in macromolecular peptide of
keratin was enhanced to varying degrees after FT. This is due
to the re-formation of hydrogen bonds between keratin molecules
during FT cycles which weakens the association between protein
molecules and water molecules.
The Raman spectra of RHK samples were observed in the
range of 4001,800 cm
(Figure 3C), where they could be
assigned to Amide I (1,5971,680 cm
), Amide III
(1,2291,310 cm
), and the S-S bond (506550 cm
2002); among them, Amide I and Amide III are very sensitive
to protein changes. The absorption peak of keratin solution at
1,684 cm
corresponds to the intermolecular cfolding structure,
which is not present in keratin hydrogels. The peaks of the Amide
III are shifted, but all of them are within the range of
1,3131,337 cm
, which is a signal of β-rotation. Compared
with keratin solution, the peak of disulde bond of RHK
hydrogel is wider, which may be related to the sulfhydryl
group being oxidized to disulde bond in the transaction
process. Notable phenomenon is that the absorption peak of
amide region at 604 cm
corresponds to the CO outside
curved surface signal becomes apparent in the RHK hydrogels.
In the XRD pattern in Figure 3D, the α-helix of RHK
hydrogels (2θ9.48°) shifted to the lower value compared
with RHK solution (2θ19.44°), especially in the FT6 and
FT9 samples. At the same time, the β-sheet of RHK hydrogels
(2θ20.06°) shifted to the higher value compared with RHK
solution (2θ19.44°). However, the variation of β-sheet of FT6
and FT9 samples was not as obvious as that of the FT3 sample.
This is perhaps because of the increase in the interactions between
keratin after several FT cycles. The interactions hindered the
α-helix to β-sheet conversion to some extent, while they provided
more chance for clustered random coils to form β-sheet.
Optical Properties of RHK Hydrogels
Figure 4A shows the result of light transmittance measurements
versus wavelength for the keratin before and after the gel. The
puried RHK solution offered high transmittance about 88% in
visible wavelengths, and the maximum transmittance of keratin
hydrogels prepared by FT can reach 67.57%. The transmittance
FIGURE 4 | (A) Optical transmittances of keratin hydrogel at varied FT cyc les, (B) photographs of the glass and keratin hydrogel, (C) DLS of keratin solution, and (D)
room temperature excitation and emission spectra.
Frontiers in Materials | August 2021 | Volume 8 | Article 7101756
Wang et al. Keratin Hydrogel Fabricated via Cryoablation
test showed that the transparency of RHK decreased with the
increase in FT cycles. Furthermore, the optical transparency of
the RHK hydrogels was examined by comparing the appearance
of these hydrogels with that of glass substrate (Figure 4B). As
shown in the gure, the appearance of hydrogels formed after
three FT cycles is similar to that of glass, and the background
handwriting can still be seen through hydrogels after nine FT
cycles. This phenomenon is rarely reported in other keratin
Pure wool keratin hydrogels concentration of 80 mg/ml
prepared by al.(Chen et al., 2021) at room temperature
showed milky white, while pure human hair keratin hydrogels
of 20 mg/ml prepared by Cui et al.(Cui et al., 2019)at20°C
showed yellowish white. Keratin hydrogels are used as medical
adjuvant, and its high transparency is conducive to observing the
healing of wounds.
The high transparency of RHK hydrogels is not only related to
the low concentration of 2% keratin but also related to the degree
of cross-linking of macromolecular chains and the uniformity of
pore size distribution in the process of gel formation (Chen 2002).
During the FT process, the three-dimensional network structure
of RHK hydrogels is formed through the cross-linking of keratin
macromolecules, and there is liquid water, uncross-linked keratin
molecules, and cross-linked regions in the hydrogels. The
existence of liquid water would not affect the transparency,
and the uncross-linked keratin molecules will have a certain
inuence on the transparency of the hydrogel (Hassan and
Peppas 2000). Therefore, the particle size of keratin was
measured as shown in Figure 4C. RHK particle size
distribution curve [G(d)] results show that the particle size of
keratin mainly concentrates between 25 and 150 nm, and the
particle size accumulation curve [C(d)] data show that the
number percentage of particle size less than 100 nm is more
than 82.5%. The particle size was less than half of the incident
light, and the substance formed was relatively transparent. It can
be seen that the small particle size and narrow distribution range
of keratin may also be one of the reasons for the formation of
transparent hydrogels. The transmittance of RHK hydrogels
decreases with the increase in FT cycles, which may be due to
the high crystallinity and surface roughness caused by the
aggregation and cross-linking of keratin molecules. At the
same time, SEM results show that the pore size is greatly
different, and the distribution of keratin hydrogels is uneven
with the increase in FT times, which will cause serious light
scattering and thus affect the transparency.
Fluorescent biomaterials have always received attention
because they can be tracked in vivo and needs no external
uorophore. Keratin is a biological material with natural
uorescent properties because it contains residues of
tryptophan, tyrosine, and phenylalanine, which absorb
ultraviolet light and emit uorescence. To study whether it
still had the inherent protein uorescence properties, we
examined the emission spectra of the keratin hydrogels.
Figure 4D shows the emission spectra of RHK solution and
hydrogels. When monitored at 354 nm, the obtained emission
spectrum of keratin solution consisted of one broad band in the
wavelength range of 280320 nm with a peak at 300 nm. The
resulting emission spectrum was composed of a broad emission
band in the wavelength range from 300 to 500 nm, and emission
peak was found to be 354 nm, which was close to uorescence
spectra of tryptophan (Burstein et al., 2001). Besides, the stoke
shift and full width at half maxima (FWHM) of the emission band
were calculated as 54 and 67 nm, respectively.
The inherent uorescence wavelength and uorescence
intensity of protein are affected by the tertiary structure of
protein, the spatial distribution of uorescent amino acids in
protein, the interaction of side chain groups with other residues
or solvents, and the energy resonance transfer within uorescent
amino acids (Ross et al., 1997). Compared with RHK solution, the
peak generates bathochromic shift in the emission spectrum of
hydrogels and the uorescence intensity is reduced. This may be
because disulde bond, hydrogen bond, ionic bond, and
hydrophobic bond are formed in the gelation process of
keratin solution, which strengthens the interaction between
proteins and reduces the amount of charge on the surface of
protein molecules, leading to the gradual exposure of the side
chain groups of uorescent amino acid molecules to the aqueous
solution. At this time, the polarity of the environment in which
the chromogenic amino acid is located gradually increases, the
extension degree of the peptide chain increases, and the content
of helical structure decreases. This was also conrmed by the
structural test results of keratin hydrogels.
The transmittance test showed that the transparency of
keratin hydrogels decreased with the increase in FT cycles.
The uorescent biomaterial test results also showed that the
more the FT cycles of keratin hydrogels, the smaller the red shift
FIGURE 5 | Compression process of RHK scaffolds.
Frontiers in Materials | August 2021 | Volume 8 | Article 7101757
Wang et al. Keratin Hydrogel Fabricated via Cryoablation
of the emission spectrum peak and the lower the uorescence
intensity. This is also related to the fact that a small amount of
water will be removed from the keratin hydrogels after multiple
FT cycles.
Compressive Properties
The compressive properties of the RHK hydrogel are presented in
Figure 5 and Figure 6. From Figure 5, the deformation of keratin
hydrogel increases continuously under the action of pressure, the
hydrogel did not break after the removal of external force when
the deformation reached more than 80%, and the deformation of
the hydrogel recovers. The reduced volume of keratin hydrogel
after deformation recovery is due to the removal of partial
unbound water under external force. It can be seen that the
keratin hydrogel has good elasticity. The compressive strength
was also signicantly increased with more freezethaw cycles
(Figure 6). The compressive stress of RHK hydrogel (FT9)
reached to 14.927 kPa when the compressive strain is 53%.
In a nutshell, low concentration and highly pure RHK hydrogels
were fabricated by green and simple freezethaw technique
without adding extraneous reagents. The morphology,
structure, and physical properties of RHK hydrogels can be
adjusted by controlling the FT processing parameters. The
RHK hydrogels shows unique optical properties, and its
transparency is up to 67.57%, while maintaining its
uorescence properties, which is conducive to the observation
of wound healing and location of drug delivery.
The original contributions presented in the study are included in
the article/supplementary material, further inquiries can be
directed to the corresponding author.
XW: data curation and writingoriginal draft. ZS: methodology,
supervision, review and editing. LZ and XS: investigation; All
authors contributed to the article and approved the submitted
This research was supported by Natural Science Foundation of
Inner Mongolia (2020LH05005), and the Foundation of Inner
Mongolia University of Technology (ZZ201817).
Almutawah, A., Barker, S. A., and Belton, P. S. (2007). Hydration of Gluten: a
Dielectric, Calorimetric, and Fourier Transform Infrared Study.
Biomacromolecules 8, 16011606. doi:10.1021/bm061206g
Belton, P. S., Colquhoun, I. J., Grant, A., Wellner, N., Field, J. M., Shewry, P. R.,
et al. (1995). FTIR and NMR Studies on the Hydration of a High-Mr Subunit of
Glutenin. Int. J. Biol. Macromolecules 17, 7480. doi:10.1016/0141-8130(95)
Burnett, L. R., Rahmany, M. B., Richter, J. R., Aboushwareb, T. A., Eberli, D., Ward,
C. L., et al. (2013). Hemostatic Properties and the Role of Cell Receptor
Recognition in Human Hair Keratin Protein Hydrogels. Biomaterials 34,
26322640. doi:10.1016/j.biomaterials.2012.12.022
Burstein, E. A., Abornev, S. M., and Reshetnyak, Y. K. (2001). Decomposition of
Protein Tryptophan Fluorescence Spectra into Log-Normal Components. I.
Decomposition Algorithms. Biophysical J. 81, 16991709. doi:10.1016/s0006-
Chen, F. S. (2002). Studies on Optical Properties and Applications of Soybean
Protein Gels. beijing: China agricultural university.
Chen, M., Ren, X., Dong, L., Li, X., and Cheng, H. (2021). Preparation of Dynamic
Covalently Crosslinking Keratin Hydrogels Based on Thiol/disulde Bonds
Exchange Strategy. Int. J. Biol. Macromolecules 182, 12591267. doi:10.1016/
Chen, R. R., and Mooney, D. J. (2003). Polymeric Growth Factor Delivery
Strategies for Tissue Engineering. Pharm. Res. 20, 11031112. doi:10.1023/a:
Chua, H. M., Zhao, Z., and Ng, K. W. (2020). Cryogelation of Human Hair
Keratins. Macromol. Rapid Commun. 41, 2000254. doi:10.1002/
Cui, X., Xu, S., Su, W., Sun, Z., Yi, Z., Ma, X., et al. (2019). Freeze-thaw Cycles for
Biocompatible, Mechanically Robust Scaffolds of Human Hair Keratins.
J. Biomed. Mater. Res. 107, 14521461. doi:10.1002/jbm.b.34237
Esparza, Y., Bandara, N., Ullah, A., and Wu, J. (2018a). Hydrogels from Feather
Keratin Show Higher Viscoelastic Properties and Cell Proliferation Than Those
from Hair and Wool Keratins. Mater. Sci. Eng. C 90, 446453. doi:10.1016/
Esparza, Y., Ullah, A., and Wu, J. (2018b). Molecular Mechanism and
Characterization of Self-Assembly of Feather Keratin Gelation. Int. J. Biol.
Macromolecules 107, 290296. doi:10.1016/j.ijbiomac.2017.08.168
FIGURE 6 | Stressstrain curve.
Frontiers in Materials | August 2021 | Volume 8 | Article 7101758
Wang et al. Keratin Hydrogel Fabricated via Cryoablation
Fu, Y., Ren, P., Wang, F., Liang, M., Hu, W., Zhou, N., et al. (2020). Mussel-inspired
Hybrid Network Hydrogel for Continuous Adhesion in Water. J. Mater. Chem.
B8, 21482154. doi:10.1039/c9tb02863c
Ge, N., Zhang, Y., Zhang, H., Zhu, R., and Shi, X. (2021). Preparation and
Characterization of Rabbit Hair Keratin Hydrogel. IOP Conf. Ser. Mater.
Sci. Eng. 1040, 012003. doi:10.1088/1757-899X/1040/1/012003
Guo, J., Pan, S., Yin, X., He, Y.-F., Li, T., and Wang, R.-M. (2014). pH-Sensitive
Keratin-Based Polymer Hydrogel and its Controllable Drug-Release Behavior.
J. Appl. Polym. Sci. 132, an. doi:10.1002/app.41572
Gupta, P., and Nayak, K. K. (2016). Optimization of Keratin/alginate Scaffold
Using RSM and its Characterization for Tissue Engineering. Int. J. Biol.
Macromolecules 85, 141149. doi:10.1016/j.ijbiomac.2015.12.010
(2017). Fabrication and Characterization of a Novel Crosslinked Human Keratin-
Alginate Sponge. J. Tissue Eng. Regen. Med. 11, 25902602. doi:10.1002/term.2159
Hassan, C. M., and Peppas, N. A. (2000). Structure and Morphology of Freeze/
Thawed PVA Hydrogels. Macromolecules 33, 24722479. doi:10.1021/
Henderson, T. M. A., Ladewig, K., Haylock, D. N., McLean, K. M., and OConnor,
A. J. (2013). Cryogels for Biomedical Applications. J. Mater. Chem. B 1,
26822695. doi:10.1039/c3tb20280a
Kim, S. Y., Park, B. J., Lee, Y., Park, N. J., Park, K. M., Hwang, Y.-S., et al. (2019).
Human Hair Keratin-Based Hydrogels as Dynamic Matrices for Facilitating
Wound Healing. J. Ind. Eng. Chem. 73, 142151. doi:10.1016/j.jiec.2019.01.017
Konop, M., Czuwara, J., Kłodzińska, E., Laskowska, A. K., Sulejczak, D., Damps, T.,
et al. (2020). Evaluation of Keratin Biomaterial Containing Silver Nanoparticles
as a Potential Wound Dressing in Full-thickness Skin Wound Model in
Diabetic Mice. J. Tissue Eng. Regen. Med. 14, 334346. doi:10.1002/term.2998
Loh, Q. L., and Choong, C. (2013). Three-dimensional Scaffolds for Tissue
Engineering Applications: Role of Porosity and Pore Size. Tissue Eng. B:
Rev. 19, 485502. doi:10.1089/ten.TEB.2012.0437
Lozinsky, V. I. (2002). Cryogels on the Basis of Natural and Synthetic Polymers:
Preparation, Properties and Application. Russ. Chem. Rev. 71, 489511.
Nakata, R., Osumi, Y., Miyagawa, S., Tachibana, A., and Tanabe, T. (2015).
Preparation of Keratin and Chemically Modied Keratin Hydrogels and
Their Evaluation as Cell Substrate with Drug Releasing Ability. J. Biosci.
Bioeng. 120, 111116. doi:10.1016/j.jbiosc.2014.12.005
Placone,J. K., Navarro, J., Laslo, G. W., Lerman, M. J., Gabard,A. R., Herendeen, G.J.,
et al. (2017). Development and Characterization of a 3D Printed, Keratin-Based
Hydrogel. Ann. Biomed. Eng. 45, 237248. doi:10.1007/s10439-016-1621-7
Ross, J. B., Szabo, A. G., and Hogue, C. W. (1997). Enhancement of Protein Spectra
with Tryptophan Analogs: Fluorescence Spectroscopy of Protein-Protein and
Protein-Nucleic Acid Interactions. Methods Enzymol. 278, 151190.
Sadeghi, S., Nourmohammadi, J., Ghaee, A., and Soleimani, N. (2020).
Carboxymethyl Cellulose-Human Hair Keratin Hydrogel with Controlled
Clindamycin Release as Antibacterial Wound Dressing. Int. J. Biol.
Macromolecules 147, 12391247. doi:10.1016/j.ijbiomac.2019.09.251
Saul, J. M., Ellenburg, M. D., de Guzman, R. C., and Dyke, M. V. (2011). Keratin
Hydrogels Support the Sustained Release of Bioactive Ciprooxacin. J. Biomed.
Mater. Res. 98A, 544553. doi:10.1002/jbm.a.33147
Shavandi, A., Silva, T. H., Bekhit, A. A., and Bekhit, A. E.-D. A. (2017). Keratin:
Dissolution, Extraction and Biomedical Application. Biomater. Sci. 5,
16991735. doi:10.1039/c7bm00411g
Sun, K., Guo, J., He, Y., Song, P., Xiong, Y., and Wang, R.-M. (2016). Fabrication of
Dual-Sensitive Keratin-Based Polymer Hydrogels and Their Controllable
Release Behaviors. J. Biomater. Sci. Polym. Edition 27, 19261940.
Sun, Z., Chen, X., Ma, X., Cui, X., Yi, Z., and Li, X. (2018). Cellulose/keratin-
catechin Nanocomposite Hydrogel for Wound Hemostasis. J. Mater. Chem. B 6,
61336141. doi:10.1039/c8tb01109e
Tang, A., Li, Y., Yao, Y., Yang, X., Cao, Z., Nie, H., et al. (2021). Injectable Keratin
Hydrogels as Hemostatic and Wound Dressing Materials. Biomater. Sci. 9,
41694177. doi:10.1039/D1BM00135C
Wang, J., Hao, S., Luo, T., Cheng, Z., Li, W., Gao, F., et al. (2017). Feather Keratin
Hydrogel for Wound Repair: Preparation, Healing Effect and Biocompatibility
Evaluation. Colloids Surf. B: Biointerfaces 149, 341350. doi:10.1016/
Wang, S., Taraballi, F., Tan, L. P., and Ng, K. W. (2012). Human Keratin Hydrogels
Support Fibroblast Attachment and Proliferation In Vitro.Cell. Tissue Res. 347,
795802. doi:10.1007/s00441-011-1295-2
Wang, S., Wang, Z., Foo, S. E. M., Tan, N. S., Yuan, Y., Lin, W., et al. (2015).
Culturing Fibroblasts in 3D Human Hair Keratin Hydrogels. ACS Appl. Mater.
Inter. 7, 51875198. doi:10.1021/acsami.5b00854
Wang, X., Shi, Z., Zhao, Q., and Yun, Y. (2021). Study on the Structure and
Properties of Biofunctional Keratin from Rabbit Hair. Materials 14, 379.
Yu, D. W. (2002). Raman Spectroscopic Analysis of the Spatial Structure and
Conformation of Peptides and Proteins. Chin. J. Anal. Lab. 21, 257261.
Zhai, M., Xu, Y., Zhou, B., and Jing, W. (2018). Keratin-chitosan/n-ZnO
Nanocomposite Hydrogel for Antimicrobial Treatment of Burn Wound
Healing: Characterization and Biomedical Application. J. Photochem.
Photobiol. B: Biol. 180, 253258. doi:10.1016/j.jphotobiol.2018.02.018
Zhang, Y., Zhao, W., and Yang, R. (2015). Steam Flash Explosion Assisted
Dissolution of Keratin from Feathers. ACS Sustain. Chem. Eng. 3,
20362042. doi:10.1021/acssuschemeng.5b00310
Zhao, Z., Moay, Z. K., Lai, H. Y., Goh, B. H. R., Chua, H. M., Setyawati, M. I., et al.
(2020). Characterization of Anisotropic Human Hair Keratin Scaffolds
Fabricated via Directed Ice Templating. Macromol. Biosci. 21, 2000314,
Conict of Interest: The authors declare that they have no known competing
nancial interests or personal relationships that could have appeared to inuence
the work reported in this paper.
Publishers Note: All claims expressed in this article are solely those of the authors
and do not necessarily represent those of their afliated organizations, or those of
the publisher, the editors, and the reviewers. Any product that may be evaluated in
this article, or claim that may be made by its manufacturer, is not guaranteed or
endorsed by the publisher.
Copyright © 2021 Wang, Shi, Zhao and Shen. This is an open-access article
distributed under the terms of the Creative Commons Attribution License (CC
BY). The use, distribution or reproduction in other forums is permitted, provided the
original author(s) and the copyright owner(s) are credited and that the original
publication in this journal is cited, in accordance with accepted academic practice.
No use, distribution or reproduction is permitted which does not comply with
these terms.
Frontiers in Materials | August 2021 | Volume 8 | Article 7101759
Wang et al. Keratin Hydrogel Fabricated via Cryoablation
For effective treatment of various diseases, pharmaceutical world require smart drug delivery systems in order to improve bioavailability, bio-degradability, site specific delivery and controlled release of drug. For this purpose, stimuli-responsive hydrogel comprised of polysaccharides chitosan and pectin, synthetic polymer polyvinylalcohol (PVA) and environment friendly coupling agent 3-aminopropyl (diethoxy)methylsilane (3-APDEMS) was fabricated. These polymers were blended and crosslinked with varying amount of crosslinker via solution casting technique. FTIR characterization elucidated the presence of chitosan, pectin and PVA functional groups as well as newly developed chemical and physical bondings. TGA showed increase in thermal stability with increase in the concentration of crosslinker. Swelling analysis depicted the successful crosslinking of polymeric chains as the swelling decreased with increase in crosslinker concentration. The change in swelling of hydrogels with change in pH of buffer media indicated the pH-dependent response of prepared stimuli responsive hydrogel. Hydrophilicity (72°) and porosity (79%) of prepared hydrogels were investigated. Furthermore, in vitro biodegradation, antibacterial and cytotoxicity analyses were also performed. The accumulative drug release was conducted in phosphate buffer saline solution and found that more than 90% of ceftriaxone was released in 180 min in controlled way that makes them ideal candidate for drug delivery and controlled release application.
Keratin is a natural protein with a high content of cysteine residues (7–13%) and is widely found in hair, wool, horns, hooves, and nails. Keratin possesses abundant cell-binding motifs such as leucine-aspartate-valine (LDV), glutamate-aspartate-serine (EDS), and arginine-glycine-aspartate (RGD), which benefit cell attachment and proliferation. It has been confirmed that keratin plays important roles in every stage of wound healing, including hemostasis, inflammation, proliferation, and remodeling, making keratin-based materials good candidates for wound dressings. In combination with synthetic and natural polymers, keratin-based wound dressings in the forms of films, hydrogels, and nanofibers can be achieved with improved mechanical properties. This review focuses on the recent development of keratin-based wound dressings. Firstly, the physicochemical and biological properties of keratin, are systematically discussed. Secondly, the role of keratin in wound healing is proposed. Thirdly, the applications of keratin-based wound dressings are summarized, in terms of the forms and functionalization. Finally, the current challenges and future development of keratin-based wound dressings are presented.
Full-text available
Protein-based hydrogel with the characters of environmentally friendly, resource saving and excellent biocompatibility has become a hot topic in the field polymer materials. In this paper, the rabbit hair keratin was extracted from waste rabbit hair ang then prepared into hydrogel by means of heating-cooling. The conclusion is that the molecular weight of rabbit hair keratin measured by SDS-PAGE concentrated in 40∼60kDa and rabbit hair keratin hydrogel in 11∼22 kDa. The forming conditions such as concentration and temperature of preparing hydrogel were experimented by using variable-controlling approach, the formation concentration of keratin should be over 125mg/ml and the temperature over 55°C. Various characterization techniques were used to determine the physical and chemical property of the hydrogel. As proved by scanning electron microscopy (SEM), covalent bonds and three-dimensional porous structure with many interconnected pores had been successfully formed. They were also characterized by thermogravimetric analysis (TG) and swelling test, etc. The consequence showed that the equilibrium moisture content can reach up to 20.21% and the swelling rate as high as 9.55%, which were inversely proportional to the concentration of keratin. Furthermore, the hydrogel had good thermal stability, the initial decomposition temperature is around 204°C. It is indicating that the excellent properties of rabbit hair keratin hydrogel can be further studied.
Full-text available
Keratin is widely recognized as a high-quality renewable protein resource for biomedical applications. A large amount of rabbit hair waste is produced in textile industries, because it has high medullary layer content, but poor spinnability. Therefore, it is of great significance to extract keratin from waste rabbit hair for recycling. In this research, an ultrasonic-assisted reducing agent-based extraction method was developed and applied to extract keratin from rabbit hair. The results showed that the ultrasonic treatment had a certain destructive effect on the structure of the fiber, and when combined with reducing agent, it could effectively promote the dissolution of rabbit hair, and extract keratin with high molecular weight between 31 and 94 kDa. The structure and properties of keratin were studied. Compared to the rabbit hair, the cystine content of keratin was significantly reduced, and the secondary structure changed from α-helix to β-sheet. The keratin products show excellent biocompatibility and antioxidant capacity. In addition, large keratin particles can be formed by assembly with a balance between intermolecular hydrophobic attraction as the concentration of urea in keratin solution decreased during dialysis.
Dynamic covalently crosslinking (DCC) hydrogels can mimic extracellular matrix and have the functions such as self-healing, self-adapting, and shape memory. The DCC keratin hydrogels based on thiol group-disulfide bonds exchange strategy have no reports so far as we know. Herein, inspired by the rich content of the intramolecular disulfide bonds and free thiol groups in the keratins extracted by reducing agents, we report a simple thiol-disulfide bonds exchange strategy for preparing the DCC keratin hydrogels. While the pH value of the keratin solution extracted by reducing agents was adjusted to 9.5–10.0, the keratin hydrogels showed the characteristic with injectability, self-healing, self-adapting, biocompatibility, and redox-responsive capacity. The extracted type II neutral/alkali keratin plays a critical role in imparting the keratin hydrogels with the reversibility behaviors due to that the keratins could build dynamic covalent bonds through thiol oxidation and disulfide exchange reactions in alkali conditions. This strategy provides an inspiration for forming DCC keratin hydrogel by avoiding the extra introduction of chemical crosslinking agents.
Injectable hydrogels hold promise in biomedical applications due to their noninvasive administration procedure and capacity enabling the filling of irregularly shaped defects. Protein-based hydrogels provide features including good biocompatibility and inherent biofunction. However, challenges still remain to develop a protein-based injectable hydrogel in a convenient way due to the limited active groups in proteins. Keratins are a group of cysteine-rich structural proteins found abundantly in skin and skin appendages. In this work, we utilized keratin and the Au(iii) salt to develop an injectable hydrogel based on the dynamic exchange between disulfide bonds (S-S) and gold(i)-thiolates (Au-S). Such a hydrogel could be prepared at the physiological pH and applied as an injectable hydrogel for biomedical applications including hemostatic and wound dressing materials. Our findings demonstrated that this keratin injectable hydrogel showed a good hemostatic effect in both tail amputation and liver injury models. Moreover, it was proved efficient as a drug loading carrier, and the deferoxamine-loaded hydrogel showed a desirable wound healing effect in a full-thickness excision wound model.
Human hair keratin (HHK) is successfully exploited as raw materials for 3D scaffolds for soft tissue regeneration owing to its excellent biocompatibility and bioactivity. However, most HHK scaffolds are not able to achieve the anisotropic mechanical properties of soft tissues such as tendons and ligaments due to lack of tunable, well-defined microstructures. In this study, directed ice templating method is used to fabricate anisotropic HHK scaffolds that are characterized by aligned pores (channels) in between keratin layers in the longitudinal plane. In contrast, pores in the transverse plane maintain a homogenous rounded morphology. Channel widths throughout the scaffolds range from ≈5 to ≈15 µm and are tunable by varying the freezing temperature. In comparison with HHK scaffolds with random, isotropic pore structures, the tensile strength of anisotropic HHK scaffolds is enhanced significantly by up to fourfolds (≈200 to ≈800 kPa) when the tensile load is applied in the direction parallel to the aligned pores. In vitro results demonstrate that the anisotropic HHK scaffolds are able to support human dermal fibroblast adhesion, spreading, and proliferation. The findings suggest that HHK scaffolds with well-defined, aligned microstructure hold promise as templates for soft tissues regeneration by mimicking their anisotropic properties.
Human hair keratins (HHK) are known for their biocompatibility and potential to regulate cell response, possibly due to the presence of the leucine‐aspartic‐valine cell adhesion and signaling motifs. Together with the abundance of cysteine residues in HHK, 3D HHK scaffolds are fabricated through cryogelation based on spontaneous disulfide crosslinks and noncovalent interactions. Herein, the molecular mechanism of HHK self‐assembly during cryogelation is interrogated and the influence of cryogelation parameters on the properties of the resultant scaffolds is studied. With successive freeze–thaw cycles, the storage modulus (G′) of HHK cryogels substantially improves from 116.4 Pa at freeze–thaw cycle 3 (FT3) to 1908.7 Pa at freeze–thaw cycle 10 (FT10). Meanwhile, it is found that complete thiol‐capping of HHK samples significantly inhibits cryogel formation as compared to partially or uncapped HHK samples, suggesting the dominant role of disulfide stabilization in cryogelation. Finally, uniaxial compression tests on HHK sponges demonstrate that FT cycling, from 0 to 10, is able to improve the compression modulus of sponges by ≈12‐folds. These findings show that macroscale properties of HHK cryogels can be conveniently modulated by physical parameters of cryogelation and that disulfide bonding is the main stabilizing force in HHK cryogels. Purified human hair keratin intermediate filament proteins crosslink naturally when subjected to successive freeze–thaw cycles (cryogelation) and are able to form 3D porous scaffolds. Modulation of cryogelation parameters such as the freezing and thawing temperature and number of freeze–thaw cycles enables tunable scaffold properties. Combined with the biocompatibility of keratin, these scaffolds can be potentially used in biomedical applications.
Mussel-inspired catechol-based strategy has been widely used in development of adhesives. However, the properties of the adhesives were still severely limited in a humid environment, especially in water. In this work, a facile and versatile approach was proposed to prepare an underwater adhesion hydrogel. First, dopamine (DA) was grafted to oxidized carboxymethylcellulose (OCMC) to obtain dopamine-grafted oxidized carboxymethylcellulose (OCMC-DA). Second, the acrylamide (AM) monomer is conjugated with OCMC-DA by Schiff base reaction, and then polymerized to form OCMC-DA/PAM hydrogel. The properties of resulting hydrogel have been fully characterized. The underwater adhesion strength of the hydrogel can reach as high as 86.3KPa and reduced to 43KPa after immersed in water for 9 days. More remarkably, we found the maximal adhesion strength was shown when the hydrogel reaches a balance between the storage modulus and loss modulus. Moreover, we demonstrate the mechanical properties of our fabricated hydrogel by compressive test and rheological analysis. The adhesive hydrogel also has excellent biocompatibility.
Keratin is a cytoskeletal scaffolding protein essential for wound healing and tissue recovery. The aim of the study was to evaluate the potential role of insoluble fur keratin-derived powder containing silver nanoparticles (FKDP-AgNP) in the allogenic full-thickness surgical skin wound model in diabetic mice. The scanning electron microscopy image evidenced the keratin surface is covered by a single layer of silver nanoparticles. Data obtained from dynamic light scattering and micellar electrokinetic chromatography showed three fractions of silver nanoparticles with an average diameter of 130, 22.5 and 5 nm. Microbiologic results revealed that the designed insoluble FKDP-AgNP dressing to some extent the growth of Escherichia coli and Staphylococcus aureus. In vitro assays showed that the FKDP-AgNP dressing did not inhibit fibroblast growth or induce hemolysis. In vivo studies using a diabetic mice model confirmed biocompatible properties of the insoluble keratin dressings. FKDP-AgNP significantly accelerated wound closure and epithelization at day 5 and 8 (p < 0.05) when compared with controls. Histological examination of the inflammatory response documented that FKDP-AgNP-treated wounds contained predominantly macrophages while their untreated variants showed mixed cell infiltrates rich in neutrophils. Wound inflammatory response based on macrophages favors tissue remodeling and healing. In conclusion, the investigated FKDPAgNP dressing consisting of an insoluble fraction of keratin which is biocompatible, significantly accelerated wound healing in a diabetic mouse model.
This study offers a new antibacterial wound dressing from carboxymethyl cellulose (CMC)-human hair keratin with topical clindamycin delivery. Keratin was successfully extracted from human hair. Different sponges fabricated by changing CMC to keratin ratio were characterized and compared. Halloysite nanotubes were used as carriers to control the clindamycin release. Various characterization techniques were used to determine the effects of keratin addition on the structure, morphology, physical properties, drug release, antibacterial activity, and cellular behavior of CMC hydrogels. As proved by SEM and EDS, porous structure with interconnected pores was successfully formed and clindamycin-loaded HNTs were uniformly dispersed within the porous structures. Increasing the keratin in CMC hydrogel not only lowered its water vapor transmission rate to a suitable range for wound healing but also improved the water stability of CMC hydrogel. The in vitro release study indicated that clindamycin was released slower in samples containing higher keratin and the Fickian diffusion mechanism controlled their release profile. The fabricated dressing effectively inhibits S. aureus bacterial colonies growth after 24 h. Fibroblast culturing on the fabricated sponges indicated that cellular attachment, proliferation, and spreading were significantly enhanced with increasing the keratin amount.
Recently, human hair-derived keratin protein has been recognized as biomaterial with high potential due to its excellent bioactivity and biocompatibility. Here, we designed human hair-derived keratin-based in situ cross-linkable hydrogels that can serve as a dynamic matrix for the enhanced wound healing. We demonstrated that our developed the keratin-based hydrogels accelerated re-epithelization and wound healing process in a full-thickness animal. Also, we investigated the molecular mechanism underlying the enhanced wound healing. In conclusion, our study proposes that human hair-derived keratin-based hydrogels with excellent bioactivity have great potential for use as a wound healing material, along with its other biomedical applications. © 2019 The Korean Society of Industrial and Engineering Chemistry